Over the years, fuels used in internal combustion engines have contained various kinds of additives to improve performance of the fuel or to alleviate problems arising during the use and combustion of fuels in internal combustion engines. During the 1950's and 1960's, engine designers generally focused their efforts towards the development of high-performance engines, with little concern about fuel economy or exhaust emissions. The fuel delivery system for engines of this era involved the use of carburetors to deliver an air-fuel mixture, via a manifold, to the cylinders for combustion. Primary concerns at this time were carburetor icing, adequate octane value, deposit formation on carburetor surfaces, fuel stability and the like. Additives for fuels such as anti-icing agents, lead-containing fuel additives, detergents, and various antioxidants generally resulted in adequate performance. Deposits in other parts of the fuel delivery system were not of a major concern because such engines were generally tuned to a rich air/fuel ratio allowing for mixture malfunction. Greater power-weight ratios meant that the driver was less apt to notice changes in peak power and fuel economy, and exhaust emissions were not a serious concern at that time.
It wasn't until the energy shortages of the 1970's, and, at about the same time, increased awareness of environmental concerns, that changes directed to purposes other than improving engine output began to receive widespread attention. During this time, and up to the early 1980's, government regulations in the United States and in other countries throughout the world imposed increasingly stringent limitations on exhaust emissions and on fuel consumption. Efforts to comply with these requirements involved various engine modifications, smaller vehicles, smaller engines, and increasingly widespread use of light weight materials. Only minor changes were made to fuel handling systems during this time other than efforts to control evaporative hydrocarbon emissions. During this time, consumers did become aware of the importance of fuel intake system cleanliness to maintain acceptable fuel consumption limits.
By the early 1980's, the carbureted internal combustion engine began to give way to throttle-body fuel injection systems. Such systems are described in U.S. Pat. Nos. 4,487,002 and 4,490,792 and in Bowler, SAE Paper 800164. Conventional fuel additives generally provided adequate service for this system.
In response to continuing demands for improved fuel economy, increased performance and reduced exhaust emissions, automobile manufacturers began to utilize even more sophisticated engines. One of the developments was the increased use of high specific output, lean burn engines. To meet the complex demands of increased power, fuel economy, and environmental control, these engines were tuned to operate at or near the lean limit of combustion, i.e., minimum amount of fuel. Lean burn engines require precise management of air-fuel ratios. This resulted in engines much less tolerant of deposits throughout the fuel metering and induction system. Thus, total fuel intake system cleanliness has become an important priority. Further developments in fuel metering and induction systems have resulted in engines that can operate efficiently and provide excellent performance while generating minimal objectionable emissions or emissions that are readily controlled with emission control systems such as catalysts and the like. One such development is the increasingly widespread use of fuel injection systems such as port fuel injection, also known as multi-port fuel injection, in which injectors discharge fuel into an intake runner or intake port. Such injector systems are illustrated in U.S. Pat. No. 4,782,808, the disclosure of which is hereby incorporated herein by reference thereto. Each injector is normally located in close proximity to the intake valve. The injector itself is designed to close tolerances and is subject to fouling, for example, from the fuel itself or because its location, in close proximity to the intake valve, is in an environment of high temperature resulting in carbon and varnish deposit formation on the injector. Such deposits result in impaired control of fuel metering. When deposits form on the injector tip, the injector may clog causing reduction in fuel flow or at least the precise fuel spray pattern is disrupted.
Another problem that has arisen is the formation of deposits on the intake valve itself. One of the reasons proposed for the particularly severe formation of deposits in port fuel injections engines is that the fuel is sprayed upon the hot valve surface resulting in formation of carbon deposits on the valve surface.
While earlier engines were sometimes prone to the formation of deposits throughout the intake system, including on the intake valve itself, the less demanding requirements of engines operating on a rich fuel mixture tended to mask the detrimental effect on driveability. Today's more sophisticated engines often are very intolerant of such deposits, resulting in severe driveability problems such as rough idling, power loss and stalling.
The use of large amounts of conventional dispersing additives in an attempt to overcome some of these stated problems often resulted in increased deposits on the intake valve and also in valve sticking. It has been proposed that degradation of the fuel additive results in deposits that impair movement of the valve.
Accordingly, efforts are continuing to provide means for maintaining intake system cleanliness or to clean up intake systems which are already contaminated.
It is one object of this invention to provide novel fuel compositions.
It is another object of this invention to provide novel fuel compositions that promote total intake system cleanliness.
It is another object to provide novel fuel compositions for use in port fuel injected engines that prevent or reduce the formation of intake valve deposits.
Another object is to provide novel fuel compositions that meet at least one of the above-stated objects and do not contribute towards valve-sticking.
A further object is to provide a method for maintaining total intake system cleanliness in a gasoline-fueled internal combustion engine.
Still another object is to provide a method for preventing or reducing the formation of intake valve deposits in a port fuel injected engine, or for removing such deposits where they have formed.
A further object is to provide a method for preventing or reducing deposits on fuel injectors, particularly, deposits at the fuel delivery nozzle thereof.
Other objects are mentioned hereinbelow or will be apparent to one skilled in the applicable art upon reading the disclosure.